A technology for performing the filter processing of blood flow velocity data having aliasing by only common filter processing means and common addition and subtraction means and actualizing image display of smooth blood flow velocity is disclosed. According to this technology, when performing image display of the blood flow velocity of blood within a subject biological body using an ultrasonic wave doppler method, the difference values of data D33 of an arbitrary focus point and data D32 and D34 of points spatially prior and subsequent to this focus point are calculated in the pre-processing unit (difference calculating unit) 41. Then, in the filtering unit 42, after filter processing is performed on these difference values, data D39 after filter processing and data D33 of the arbitrary focus point are added in the post-processing unit (addition processing unit) 43. In this way, a filter processing can be performed under the assumption that the velocity difference is smaller than the velocity difference generated by the aliasing phenomenon, and filter processing of the blood flow velocity value in the sound ray direction of the ultrasonic waves can be performed without being influenced by aliasing.
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1. An ultrasonic doppler blood flow measuring device, comprising: a velocity calculating unit for calculating a blood flow velocity value of a blood within a subject biological body from a doppler-shift detected from echo signals of ultrasonic pulses transmitted to said subject biological body; and
a blood flow velocity filter means for performing filter processing of said blood flow velocity value outputted from said velocity calculating unit without being influenced by aliasing, wherein
the blood flow velocity filter means comprises:
a first difference calculating means for subtracting a first blood flow velocity value of a first focus point adjacent to an arbitrary focus point supplied to said blood flow velocity filter means from a blood flow velocity value of said arbitrary focus point supplied to said blood flow velocity filter means and calculating a first difference value thereof;
a second difference calculating means for subtracting said blood flow velocity value of said arbitrary focus point supplied to said blood flow velocity filter means from a second blood flow velocity value of a second focus point adjacent to said arbitrary focus point supplied to said blood flow velocity filter means and calculating a second difference value thereof;
a filter means for performing filter processing on said first and second difference values; and
an addition processing means for adding said blood flow velocity value of said arbitrary focus point to a filter processing result from said filter means,
wherein said filter means comprises:
a first multiplier for multiplying said first difference value by a coefficient;
a second multiplier for multiplying said second difference value by a coefficient; and
an adder for adding outputted data from said first and second multipliers, and
wherein said first and second difference calculating means and said adder perform a fixed decimal point calculation.
2. The ultrasonic doppler blood flow measuring device according to
3. The ultrasonic doppler blood flow measuring device according to
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The present invention relates to an ultrasonic Doppler blood flow measuring device which measures blood flow within a biological body by using the Doppler phenomenon of ultrasonic waves and performs image display regarding the measured results, in the medical field, and more particularly, relates to an ultrasonic Doppler blood flow measuring device for showing, by color display, an image according to the blood flow rate data generated by the aliasing phenomenon.
Conventionally, an ultrasonic Doppler blood flow measuring device (color flow device), which enables measurement of blood flow distribution and blood flow velocity within a biological body by using the Doppler phenomenon of ultrasonic waves and displays the blood flow velocity, in correspondence to a predetermined color, by superimposing a black and white, two-dimensional cross-sectional image therewith, is known.
The Doppler-shift signal is supplied from the phase detecting unit 4 to a wall filter 5. In wall filter 5, signals from unnecessary tissues which are low-frequency signal components are removed, and furthermore, in a velocity calculating unit 6, blood flow information, such as blood flow velocity data, blood echo intensity data, blood flow velocity variance data, and the like, is determined based on the signal subsequent to processing by the wall filter 5. This blood flow information is smoothing-processed by a filter 7, supplied to a digital scan Converter (DSC) 8, and coordinate-converted into a shape adhering to ultrasonic scanning.
In addition, a B-mode image (ultrasonic cross-sectional image) signal (B-mode signal) is supplied from an envelope detecting unit 9 to DSC 8, in the same way, and the DSC 8 not only coordinate-converts the supplied image data into a shape adhering to ultrasonic scanning, but also combines B-mode signal and blood flow information and shows a two-dimensional blood flow image on a monitor 10.
The blood flow velocity data comprised in the blood flow information is data which has a possibility of generating an aliasing phenomenon based on the Nyquist theorem. With regards to this measurement of blood flow velocity data having this aliasing, a method, for example, for performing filter processing with an arbitrary order after determining aliasing and performing corrections is disclosed in the following Patent Document 1 as a method for filter processing in filter 7.
Patent Document 1: Japanese Patent Application Publication No. 4-161146 (Heisei)
However, in the filter processing method for blood flow velocity data disclosed in Patent Document 1, the aliasing determination method and the aliasing correction method are complicated, and this is problematic in that, in order to actualize this filter processing method, a complicated hardware configuration is required.
In light of the foregoing problems, an object of the present invention is to provide an ultrasonic Doppler blood flow measuring device which actualizes the filtering of blood flow velocity data having aliasing and performing a screen display of blood flow velocity which changes smoothly, spatially and temporally.
In order to achieve the foregoing object, the ultrasonic Doppler blood flow measuring device of the present invention has a blood flow velocity filter means for performing filter processing in order to calculate the blood flow velocity value of the blood within a subject biological body from the echo signals of ultrasonic pulse transmitted to the subject biological body, wherein
the blood flow velocity filter means comprises:
a difference calculating means for subtracting the focus point blood flow velocity value of an arbitrary focus point from the blood flow velocity value supplied to the blood flow velocity filter means and calculating the difference value thereof;
a filter means for performing filter processing on the difference values; and
an addition processing means for adding the focus point blood flow velocity value to the filter processing result from the filter means.
According to this configuration, it becomes possible to perform filter processing of blood flow velocity data which has aliasing by only common filter means and common addition and subtraction means, and a smooth image display of blood flow velocity can be actualized.
Furthermore, the ultrasonic Doppler blood flow measuring device of the present invention is configured such that the difference calculating means calculates the difference value of consecutive point blood flow velocity value of a point which is spatially consecutive to the arbitrary focus point and the arbitrary focus point blood flow velocity value.
According to this configuration, when performing an image display of the blood flow velocity of the blood flowing within the subject biological body, it becomes possible to reduce spatial random noise within one image frame and a smooth image display of blood flow velocity can be actualized.
Furthermore, the ultrasonic Doppler blood flow measuring device of the present invention is configured such that the difference calculating means calculates the difference value of the blood flow velocity value which is temporally consecutive to the arbitrary focus point and the arbitrary focus point blood flow velocity value.
According to this configuration, when performing an image display of the blood flow velocity of the blood flowing within the subject biological body, it becomes possible to reduce temporal random noise between a plurality of image frames and a smooth image display of blood flow velocity can be actualized.
The ultrasonic Doppler blood flow measuring device of the present invention has a blood flow velocity filter means for performing filter processing to calculate the blood flow velocity value of the blood flowing within the subject biological body from the echo signals of the ultrasonic pulse transmitted to the subject biological body, wherein the blood flow velocity filter means comprises a difference calculating means for subtracting the focus point blood flow velocity value of an arbitrary focus point from the blood flow velocity value supplied to the blood flow velocity filter means and calculates the difference value thereof,
a filter means for performing filter processing on the difference value, and an addition processing means for adding the focus point blood flow velocity value to the filter processing result from the filter means, and has an effect, wherein the filter processing of blood flow velocity data which has aliasing is preformed by only common filter means and common addition and subtraction means, and a smooth image display of blood flow velocity is actualized.
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An ultrasonic Doppler blood flow measuring device according to first and second embodiments of the present invention is described hereafter, with reference to the drawings.
First, the first embodiment of the present invention is described.
The connection configuration of respective constituent elements within the spatial filter 20 shown in
When data D32 provided from the latch 21 is provided, the latch 22 also holds this data D32 and provides the held data (for example, data of the previous focus point) D33 to the latch 23 and the adder 24, 25, and 29, as well. Furthermore, when data D33 provided from the latch 22 is provided, the latch 23 also holds this data D33 and provides the held data D34 to the adder 25. In this way, data D32, D33, and D34 of spatially consecutive focus points are output to the pre-processing unit 41 at the same timing from the latches 21, 22, and 23, respectively.
In addition, between the latches 21, 22, and 23 and the adders 24 and 25, the output of the latch 21 is connected to the input on the addition side of the adder 24, the output of the latch 22 is connected to the input of the subtraction sides of the adder 24 and 25, respectively, and the output of the latch 23 is connected to the input on the addition side of the adder 25. In this way, the adder 24 receives data D32 from the addition side and data D33 from the subtraction side, respectively, performs calculation, and outputs the result of subtracting data D33 from data D32 to the multiplier 26 as data D35. In addition, the adder 25 receives data D34 from the addition side and data D33 from the subtraction side, respectively, performs calculation, and outputs the result of subtracting data D33 from data D34 to the multiplier 27 as data D36.
The multipliers 26 and 27 multiply the provided data by the filter coefficients set respectively to the provided data and outputs the results. Therefore, the multiplier 26 multiplies filter coefficient k1 and data D35 provided from the adder 24 and outputs data D37, and the multiplier 27 multiplies filter coefficient k3 and data D36 provided from the adder 25 and outputs data D38. The adder 28 receives data D37 and D38 from the multipliers 26 and 27, adds these data, and outputs the added result to the adder 29 as data D39. Then, the adder 29 receives data D33 from the latch 22 and data D39 from the adder 28, respectively, adds these data, and outputs the added result to the DSC 8 as data D40.
The spatial filter 20 according to the present embodiment is a one-dimensional filter and a second order filter. In other words, in the present embodiment, the focus sample data D33 is subtracted from the consecutive point blood flow velocity value (data D32 and D34), which is consecutively before and after the focus point. Data D35 and D36, where focus sample data D33 is the origin (in other words, 0), are created by the pre-processing unit 41 composed of adders 24 and 25, with the focus point as data (focus sample data or focus point blood flow velocity value) D33 which is output from the latch 22.
The pre-processing unit 41, the filtering unit 42, and the post-processing unit 43 operate as a second order FIR (Finite duration Impulse Response) filter, by the combination thereof.
The filter operation of the present invention is described using equations.
If output data D40 is expressed using respective data in
[Equation 1]
D40=D39+D33
D40=D37+D38+D33
D40=k1*D35+k3*D36+D33
D40=k1*(D32−D33)+k3*(D34−D33)+D33
D40=k1*D32+(1−k1−k3)*D33+k3*D34 Equation 1
From equation 1,
[Equation 2]
H(z)=k1+(1−k1−k3)z^(−1)+k3z^(−2) Equation 2
Here, z^(−n) is an operator indicating the lag element of n column.
This FIR filter is given low-pass filter characteristics in order to eliminate random noise having high-frequency component. Therefore, as the second order FIR filter, it is preferable that all coefficients are positive numbers,
and are set to:
[Equation 3]
φ<k1, φ<k3, and k1+k3<1 Equation 3
In addition, the adders 24 and 25 perform, for example, a fixed decimal point calculation, the output data format is the same as the input data format, and the carry bit of the addition result is omitted (ignored). For example, if the input has an 8-bit 2's complement format, the output also has an 8-bit 2's complement format. Thus, data D35 is calculated as the difference value of data D32 and focus sample data D33, under the condition that the velocity difference between data is a smaller velocity difference than the velocity difference which causes aliasing. Similarly, data D36 is calculated as the difference value of data D34 and focus sample data D33, under the condition that the velocity difference between data is a smaller velocity difference than the velocity difference which causes aliasing.
By the foregoing processing, it becomes possible to perform filter calculation of the consecutive point blood flow value (three data D32, D33, and D34) provided to the second order FIR filter, with one data among these as the focus sample data (for example, data D33), under the assumption that the velocity difference between the blood flow velocity value of the focus sample data and the blood flow velocity data of other data is a smaller velocity difference than the velocity difference which causes aliasing. Therefore, at the same time (within the same image), after the difference value of an arbitrary center pixel is filter processed, it becomes possible to, again, add data on the arbitrary center pixel and obtain data on the desired blood flow velocity value, and spatial random noise can be reduced. Although the foregoing first embodiment was an example actualizing a one-dimensional second order filter, it is possible make an extension to a one-dimensional and two-dimensional, high-order filter, in the same way.
As described above, according to the ultrasonic Doppler. blood flow measuring device according to the first embodiment of the present invention, by providing the spatial filter 20 having the pre-processing unit 41 for performing subtraction with the focus sample data D33 as the origin and the filtering unit 42 for performing filter processing on all provided data, and the post-processing unit 43 for adding the focus sample data D33 to the output data D39 after filter processing by the filtering unit 42, it becomes possible to perform filter processing of blood flow velocity data (consecutive point blood flow velocity value) which are spatially consecutive in the acoustic scan line of ultrasound, without being influenced by aliasing, and a spatially smooth blood flow velocity image can be provided.
Next, a second embodiment of the present invention is described.
The connection configuration of respective constituent elements within the frame filter 50 shown in
After the input signal D61 of the blood flow information from the velocity calculating unit 6 is provided to the latch 21, the signal is further provided to the frame memory 52 as data D62. The frame memory 52 holds data D62 provided from the latch 21 and outputs data D63 of the one frame prior thereto in the same region, as well. In addition, the frame memory 53 similarly holds data D63 output from the frame memory 52 and outputs data D64 of the one frame prior thereto in the same region (two frames before data D62), as well. Thus, data D62, D63, and D64 of the same region within temporally consecutive frames (in other words, blood flow velocity values temporally consecutive to the arbitrary focus point) are output to the pre-processing unit 41 at the same timing from the latch 21 and the frame memories 52 and 53, respectively. In this case, data D63 is used as the focus sample data (focus point blood flow velocity value), and the same processing as that in the foregoing first embodiment is performed in the pre-processing unit 41, the filtering unit 42, and the post-processing unit 43.
By the foregoing processing, it becomes possible to perform filter calculation of the three data, D62, D63, and D64, provided to the second order FIR filter, with one data among these as the focus sample data (for example, data D63), under the assumption that the velocity difference between the blood flow velocity value of the focus sample data and the blood flow velocity data of other data is a smaller velocity difference than the velocity difference which causes aliasing. Therefore, after the difference value of data on the blood flow velocity value at an arbitrary time and the data on the blood flow velocity value which is temporally prior and subsequent thereto is filter processed, in the same region, it becomes possible to, again, add data on the blood flow velocity value at a predetermined time and obtain data on the desired blood flow velocity value, and temporal random noise between a plurality of temporally consecutive images can be reduced.
As described above, according to the ultrasonic Doppler blood flow measuring device according to the second embodiment of the present invention, by providing the frame filter 50 having the pre-processing unit 41 for performing subtraction with the focus sample data D63 as the origin and the filtering unit 42 for performing filter processing on all provided data, and the post-processing unit 43 for adding the focus sample data D63 to the output data after filter processing by the filtering unit 42, it becomes possible to perform filter processing of blood flow velocity data (blood flow velocity value temporally consecutive to arbitrary focus point) which are temporally consecutive in the same region in the acoustic scan line of ultrasound without being influenced by aliasing, and a temporally smooth blood flow velocity image can be provided. Although the foregoing second embodiment was an example actualizing a second order frame filter, it is possible make an extension to a filter of a higher order, in the same way.
Although the frame filter 50 is provided between the velocity calculating unit 6 and the DSC 8 in the foregoing second embodiment, it can be provided between the DSC 8 and the monitor 10, as well. In addition, although the ultrasonic Doppler blood flow measuring device having the spatial filter 20 was described in the first embodiment and the ultrasonic Doppler blood flow measuring device having the frame filter 50 was described in the second embodiment, separately, it is also possible to provide both the spatial filter 20 and the frame filter 50 within the ultrasonic Doppler blood flow measuring device. Furthermore, although the spatial filter 20 and the frame filter 50 are configured by hardware in the first and second embodiments, the filter processing performed by these filters can also be actualized by software programs.
The ultrasonic Doppler blood flow measuring device according to the present invention can actualize filtering of blood flow velocity data having aliasing by a simple, small-scale algorithm and perform image display of blood flow velocity which changes smoothly, spatially or temporally, and in the medical field, can be applied to technology for measuring the blood flow within a biological body sing the Doppler phenomenon of the ultrasonic waves and performing image display related to this measured result, as well as, in particular, applied to technology for color-displaying image of blood flow velocity data generated by the aliasing phenomenon.
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